Regional cerebral blood flow of the main visual pathways during photic stimulation of the retina in intact and split-brain monkeys

Capillary level imaging of local cerebral blood flow in bicuculline-induced epileptic foci

Local hemodynamics of the cerebral cortex is the basis of modern functional imaging techniques, such as fMRIand PET. Despite the importance of local regulation of the blood flow, capillary level quantification of cerebral blood flow has been limited by the spatial resolution of functional imaging techniques and the depth penetration of conventional optical microscopy. Two-photon laser scanning microscopic imaging technique has the necessary spatial resolution and can image capillaries in the depth of the cortex. We have loaded the serum with fluorescein isothiocyanate dextran and quantified the flow of red blood cells (RBCs) in capillaries in layers 2/3 of the mouse somatosensory cortex in vivo. Basal capillary flux was quantified as approximately 28.9+/-13.6 RBCs/s (n=50, mean+/-S.D.) under ketamine-xylazine anesthesia and 26.7+/-16.0 RBCs/s (n=31) under urethane anesthesia. Focal interictal (epileptiform) activity was induced by local infusion of bicuculline methochloride in the cortex. We have observed that capillary blood flow increased as the cortical local field events developed into epileptiform in the vicinity of GABA receptor blockade (<300 microm from the administration site). Local blood flow in the interictal focus increased significantly (42.5+/-18.5RBCs/s, n=52) relative to the control conditions or to blood flow measured in capillaries at distant (>1mm from the focus) sites from the epileptic focus (27.8+/-12.9 RBCs/s, n=30). These results show that hyper-synchronized neural activity is associated with increased capillary perfusion in a localized cortical area. This volume is significantly smaller than the currently available resolution of the fMRI signal.

Noninvasive functional imaging of human brain using light

Analysis of photon transit time for low-power light passing into the head, and through both skull and brain, of human subjects allowed for tomographic imaging of cerebral hemoglobin oxygenation based on photon diffusion theory. In healthy adults, imaging of changes in hemoglobin saturation during hand movement revealed focal, contralateral increases in motor cortex oxygenation with spatial agreement to activation maps determined by functional magnetic resonance imaging; in ill neonates, imaging of hemoglobin saturation revealed focal regions of low oxygenation after acute stroke, with spatial overlap to injury location determined by computed tomography scan. Because such slow optical changes occur over seconds and co-localize with magnetic resonance imaging vascular signals whereas fast activation-related optical changes occur over milliseconds and co-localize with EEG electrical signals, optical methods offer a single modality for exploring the spatio-temporal relationship between electrical and vascular responses in the brain in vivo, as well as for mapping cortical activation and oxygenation at the bedside in real-time for clinical monitoring.

Interactions between electrical activity and cortical microcirculation revealed by imaging spectroscopy: implications for functional brain mapping

Modern neuroimaging techniques use signals originating from microcirculation to map brain function. In this study, activity-dependent changes in oxyhemoglobin, deoxyhemoglobin, and light scattering were characterized by an imaging spectroscopy approach that offers high spatial, temporal, and spectral resolution. Sensory stimulation of cortical columns initiates tissue hypoxia and vascular responses that occur within the first 3 seconds and are highly localized to individual cortical columns. However, the later phase of the vascular response is less localized, spreading over distances of 3 to 5 millimeters.

Control of blood flow in the cat spinal cord

Spinal cord blood flow (SCBF) and the effect of end-tidal CO2 concentration (ETCO2) on SCBF (CO2 reactivity) were studied in the lumbar spinal cord of cats by means of the hydrogen-clearance technique Hydrogen gas was administered by inhalation, and its level in spinal cord tissue was estimated amperometrically with small (75 micrometers) platinum electrodes. The average SCBF's at normocapnia (ETCO2 = 4%) of the ventral horn gray matter and of the white matter at several locations were 43.2 and 16.2 ml . 100 gm-1 . min-1, respectively. For gray and white matter, the values of CO2 reactivity, estimated by the coefficient of the regression of SCBF (ml . 100 gm-1 . min-1) on ETCO2 (ml . 100 ml-1) were 11.6 and 2.1, respectively. No differences in SCBF or CO2 reactivity were observed between intact animals kept under N2O-O2 ventilation and decerebrated animals with no anesthesia. After an acute spinal section, ventral horn SCBF and CO2 reactivity (measured eight segments below the cordotomy) were not altered, in spite of the profound neural depression present (that is, spinal shock). Orthodromic (dorsal root) stimulation of the ventral horn neurons induced an average increase in blood flow of 128% above control values. Antidromic (ventral root) motoneuron activation failed to produce any significant changes in ventral horn blood flow.

Metabolic mapping of the brain's response to visual stimulation: studies in humans

These studies demonstrated increasing glucose metabolic rates in the human primary (PVC) and associative (AVC) visual cortex as the complexity of visual scenes increased. The metabolic response of the AVC increased more rapidly with scene complexity than that of the PVC, indicating the greater involvement of the higher order AVC for complex visual interpretations. Increases in local metabolic activity by as much as a factor of 2 above that of control subjects with eyes closed indicate the wide range and metabolic reserve of the visual cortex.

Local cerebral glucose utilization in newborn and pubescent monkeys during focal motor seizures

The [14C]deoxyglucose method was used to determine the rate of local cerebral glucose utilization (LCGU) in newborn and pubescent monkeys during focal motor seizures induced by injecting penicillin into the face-hand area of the right motor cortex. Seizures were studied in 3 newborn and 6 pubescent monkeys, and 3 newborn and 4 pubescent monkeys were used as controls. In controls, the pattern of glucose utilization within structures of the sensorimotor system was quite differenet at the two age levels; newborns showed far less activity, especially in the neocortex and striatum. In the monkeys with seizures, the unilateral increase in LCGU relative to the controls was greater in newborn than in pubescent monkeys except in the cerebral and cerebellar cortices. The increased glucose utilization in cortical and subcortical structures of the newborns was ipsilateral to the discharging lesin and lacked the well-defined pattern seen in the pubescent monkeys. In general, newborn brain was capable of supporting a focal motor seizure but lacked the precise clinical and electrographic expressions or efficient energy metabolism that accompany maturation of the brain at puberty.

Coupling between neuronal activity and focal blood flow in experimental seizures

Local blood flow, ECoG and single cortical neurone activity were recorded simultaneously from single microelectrodes in 17 cats. Seizures were induced by repeated intravenous injections of pentylenetetrazol (PTZ, 10-20 mg/kg) or by local application of 1 M Na-penicillin. Seven to 20 sec after appearance of burst activity in cortical neurones and ECoG, focal flow increased up to 300% of control. The extent of this flow increase was significantly correlated with the change in firing rate of the neurones. With cessation of seizure activity the flow returned to or below control values. Forty to 70 mg/kg PTZ caused status epilepticus with high voltage rhythmic discharges lasting 30 min-2 h. In 3 cats with status, the flow decreased below control despite persisting seizures, indicative of uncoupling between activity and flow. The delayed coupling between activity and flow during drug-induced seizures indicates a metabolic mediator. Uncoupling observed in cases with long lasting seizures may be due to brain oedema following increased permeability of the blood-brain barrier.

XIII. Cerebral circulation and metabolism in stroke. Cerebral circulation and metabolism in stroke study group

An understanding of the cerebral circulation is so fundamental to comprehension of the pathogenesis of stroke that cerebral blood flow and metabolism merit review in this series of reports. The authors recognize that the research described here is very technical in nature and may appear to have little practical application to clinical medicine. Nevertheless, these matters are basic to the development of precise methods for the measurement of regional cerebral blood flow in man which could be used to monitor the therapy of stroke with greater success than is possible at present.

Regional cerebral blood flow in delayed brain swelling following x-irradiation of the right occipital lobe in the monkey

Four to 5 months after exposure of the right occipital lobe of the monkey to 3500 rads of X-irradiation there is a proliferative and degenerative lesion accompanied by a massive break in the blood-brain barrier. The resulting vasogenic edema causes gross swelling in the ipsilateral hemisphere, compression of the contralateral hemisphere with ventricular dilatation, and distortion of midline structures, which may result in herniation through the incisura and foramen magnum. The regional cerebral blood flow, determined by [14C]antipyrine method, at successive stages in the development and resolution of the delayed brain swelling shows a reduction of blood flow in white and gray matter, first regionally, then throughout the ipsilateral hemisphere and finally throughout the brain. This is accompanied by an increase in CSF pressure, CSF lactic dehydrogenase and total protein, and clinical signs of increased intracranial pressure. With resolution of CSF pressure, there is a return to baseline of CSF chemistry and partial resolution of the other parameters. The cerebral blood flow shows a greater recovery in gray than white matter, but there remains a diffuse depression suggesting a long-term impairment in cellular metabolism and/or blood flow regulatory mechanisms.